Modern and future magnetic storage drive platters need precise writer and reader lapping geometry control (e.g., less than or equal to about 3 nm for one sigma) for the magnetic transducers or sliders. Current reader to writer overlay alignment at wafer level, as measured by wafer fabrication, is insufficient (e.g., greater than 5 nm for one sigma). The measurement of overlay between successive patterned layers on a wafer is one of the most important process control techniques used in the manufacturing of integrated circuits and devices such as sliders. Overlay generally pertains to the determination of how accurately a first patterned layer (e.g., reader layer) aligns with respect to a second patterned layer (e.g., writer layer) disposed above or below it. Overlay is described in greater detail in U.S. Pat. No. 7,804,994, the entire content of which is incorporated herein by reference.
The “as printed” overlay sigma, as discussed above, results in the inability to meet both the reader and writer lapping height requirements. For example, if the desired reader height is obtained, then writer height is sacrificed and vice versa. Current lapping technology utilizes three axis correction. A first axis relates to the balance used to keep the row bar height on both ends equal during lapping cycle. A second axis relates to the bending of the bar in between the sliders positioned at the ends of the bar. A third axis relates to the tilting of the row bar to increase or decrease the writer removal relative to the reader removal. Various lapping technology including the third axis tilting of the row bar for correction is described in U.S. Pat. No. 7,681,303, the entire content of which is incorporated herein by reference.
Historically lapping tools have been designed such that great effort, thought, modeling and trial and error are invested to ensure the row bar does not twist during the lapping cycle due to bending, balancing and lapping shear forces. This is because it is thought to be well known that row bar twisting will compromise the reader/writer overlay.